The HMG-CoA reductase inhibitors (Statins) have been used in reducing blood levels of LDL cholesterol. Cholesterol is produced via the mevalonic acid pathway. Reducing the formation of mevalonic acid, a precursor to cholesterol, leads to a corresponding decrease in hepatic cholesterol biosynthesis with a reduction in the cellular pool of cholesterol. The HMG-CoA reductase inhibitors (Statins) represented by the following general Formula-I,

wherein R is a residue of HMG-CoA reductase inhibitor; M represents hydrogen or pharmaceutically acceptable salts like sodium, potassium, magnesium and calcium.
Bis[(E)-7-[4-(4-fluorophenyl)-6-isopropyl-2-[methyl(methylsulfonyl)amino]pyrimidin-5-yl](3R,5S)-3,5-dihydroxyhept-6-enoic acid]Calcium Salt of Formula-A (Rosuvastatin Calcium) is an HMG-CoA reductase inhibitor, developed by shionogi for the treatment of hyperlipidemia.

Rosuvastatin calcium is marketed under the proprietary name CRESTOR for treatment of mammals such as human and administrated as daily dosage form of 5 mg, 10 mg, 20 mg and 40 mg.
Rosuvastatin and its pharmaceutically acceptable salts were first disclosed in European patent publication EP 0521471. It also discloses process for the preparation of Rosuvastatin calcium.
Bis{(3R,5S,6E)-7-[2-cyclopropyl-4-(4-fluorophenyl)-3-quinolyl]-3,5-dihydroxy-6-heptenoate} monocalcium of Formula-B (Pitavastatin Calcium) is an HMG-CoA reductase inhibitor, developed by Nissan Chemical Industries for the treatment of hyperlipidemia.

Pitavastatin and its pharmaceutically acceptable salts were first disclosed in European patent publication EP 0304063. It also discloses process for the preparation of Pitavastatin sodium.
U.S. Pat. No. 5,260,440 and PCT publication No. WO 03/097614, disclose the synthesis of Rosuvastatin from the intermediate 3(R)-3(tert-butyldimethylsilyloxy)-5-oxo-6-triphenyl-phosphoranylidene hexanoate.
PCT publication No. WO 03/087112 discloses the synthesis of Rosuvastatin from intermediate, (3R)-3-(t-butyldimethylsilyloxy)-6-dimethoxyphosphinyl-5-oxo-hexanoate.
U.S. Pat. No. 5,117,039 discloses the process for the preparation of (3R)-3-[(tert-butyldimethylsilyl)oxy]pentanedioic acid, 1-[(R)-Mandelic acid]Ester by the ring opening of 3-[(tert-Butyldimethylsilyl)oxy]pentanedioic anhydride using benzyl D-mandelate which gives less yields along with impurities.
US 20090076292 discloses process for the preparation of Rosuvastatin by using the intermediates 3(R)-3(tert-butyldimethylsilyloxy)-5-oxo-6-triphenyl-phosphoranylidene hexanoate and (3R)-3-(t-butyldimethylsilyloxy)-6-dimethoxyphosphinyl-5-oxo-hexanoate. These intermediates are prepared by a novel intermediate i.e. chiral base salt of hydroxy protected diethyl glutarate.
US 2005/0070605 A1 discloses the enantioselective opening of 3-hydroxy protected glutaric anhydride by phenylethylamine to form an amide bond, and further conversion to obtain the HMG-CoA reductase inhibitor.
The compound 3(R)-3(tert-butyldimethylsilyloxy)-5-oxo-6-triphenyl-phosphoranylidene hexanoate can be prepared from the pentanoic acid derivatives of the following Formula-II.

wherein X is hydrogen or hydroxy protecting group and R1 is carboxyl protecting group.
In prior art compound of Formula-II is prepared by the resolution of the racemate or asymmetric synthesis. These routes have disadvantages in the industrial scale preparation. The present invention provides an industrially scalable process for the pentanoic acid derivatives of Formula-II and further conversion to HMG-CoA reductase inhibitors.